The present invention relates to a digital communication network, more particularly, to a system for linking a group of channels (a channel group) between two terminals. The channels in the channel group are connected in the same order at each terminal, even though the digital telephone switching network connecting the terminals is not required to keep the channels in order.
Recently, the demand for non-telephone data transmission such as high speed data communication, facsimile or image transmission, is increasing. These services require a broader band data link than that of a telephone channel. Meanwhile, the movement to digitize existing telephone networks is progressing. As a result, data transmission networks and digital telephone networks are constructed differently from each other. The present invention intends to provide a data transmission system which can utilize a digital telephone network as a data transmission network and improve the utilization of digital telephone systems by data communication equipment.
A telephone switching system, whether it is an analog system or digital system, is based on the principle that the channel which links two terminals is established by selecting one channel out of a group of idle trunks, and switching (connecting) them to a terminal (telephone) for each call. Therefore, the channel path, selected by switching equipment located between two terminals and used to link them, is different from call to call.
In prior art technology, in order to link a channel a group between two terminals (group connection) keeping a specific relationship between each channel (space order), a specific control signal was used for the switching systems to bundle the channels in the specific order. Such specially controlled channel switching networks can not be used for general purpose communications, because they are idle at all times except during the special use. Therefore, such special connection of channel groups is not desirable, from the view point of channel utilization.